Automatic gain control (AGC) circuits are widely used to achieve controlled signal amplification in electronic systems. In a typical prior-art AGC circuit, depicted in FIG. 1, an input signal 102 is amplified by a variable-gain amplifier 101 (VGA) to produce an amplified signal 104 that is both output from the AGC circuit and supplied to a gain control loop 103. The gain control loop 103 conventionally includes an envelope detector 105 to detect the peak amplitude of the amplified signal 104, and a comparator 107 to compare the peak amplitude to a desired amplitude 108 and thus generate an error signal 106 that is applied within a filter circuit 109 to adjust the gain of the variable-gain amplifier 101 (i.e., adjust a gain control signal 110) in a direction counter to the error. Thus, the variable-gain amplifier 101 and gain control loop 103 collectively form a negative-feedback circuit that attempts to minimize the error between the desired and amplified signal levels, thereby achieving a desired signal amplification.
One major drawback to the AGC circuit of FIG. 1, is that the gain control loop 103 operates without interruption and thus consumes power continuously. Such continuous power consumption renders the AGC circuit of FIG. 1 increasingly unsuitable for application in the power-constrained environment of modern integrated circuits (ICs) and electronics devices, and particularly in modern IC signaling interfaces where thermal considerations and ever-increasing input/output (I/O) count continue to shrink I/O power budgets.